The present invention relates to the art of non-contact data linking, particularly the communication of data between structures which are moving relative to one another. The invention finds particular application in conjunction with the transfer of data between moving and stationary gantry portions of CT scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention also find application in conjunction with data transfer and/or communication in other environments.
Typically, a patient is positioned in a supine position on a horizontal couch through a central bore of a stationary gantry of a CT scanner. An imaging x-ray tube is mounted on a rotatable gantry portion and rotated around the patient and central bore. Slip ring assemblies provide data and power communication between the rotating and stationary gantry portions. Arrays of brush assemblies are positioned to make electrical contact with the slip ring in order to provide an electrical path for the transfer of data and communication signals between the stationary and rotating gantries.
Prior art brush assemblies use brushes which are delicate and easily damaged. Often, individual brush assemblies are not replaced and the whole relatively expensive brush block must be replaced. Under rotation opposite the usual direction, the brushes may hang up, buckle, and experience sudden catastrophic failure. In applications such as CT scanners, redundant bulky cartridges are often employed. The use of only one brush per ring tends to cause loss of communication due to skipping. When a brush is biased against the slip ring by a relatively large force to reduce skip, brush life is reduced due to the frictional wear between the brush and slip ring. The increased biasing also tends to cause hang ups or stick. Further, dust and contaminants settle on the exposed slip rings leading to noise, particularly noticeable in high speed communications. This leads to costly maintenance and the need for replacement parts.
More recently, another type of data link has been proposed which has implications for CT scanners. A fluorescent optical rotary joint is a non-contact data link whereby modulated light from an LED is fed laterally into an optical fiber to excite an imbedded fluorescent dye along the length of the fiber. Light which is emitted from the fluorescent dye at relatively flat angles with regard to the longitudinal direction of the fiber is subject to total internal reflection and is launched down the length of the fiber. In one type of prior art data link, the optical fiber is a continuous loop and the LED is rotated relative to the loop. However, this type of data link is accompanied by some inherent drawbacks. Dust, dirt, or other contaminants on the outer surface of the optical fiber interfere with the coupling of light from the LED as it is laterally fed into the optical fiber. This introduces noise into the signal and attenuates the signal, limiting dynamic range. Furthermore, there must be extremely accurate alignment between the LED and fiber. Care must be taken the prevent wobble and to keep the optical path between the LED and fiber optic free of obstruction. The delicate fiber is exposed not only to damage and dirt, but also to external ambient and stray light which can excite the dye and be launched down the fiber creating noise, inaccuracy, and false signals.
The present invention contemplates new and improved non-contact data link assemblies which overcome the above-referenced problems and others.